This invention relates to a seed germination medium for encouraging the germination and establishment of seeds, especially in hostile environments, where water, nutrients, climate, chemical contamination and soil conditions may be limiting factors.
Desertification, salination and soil erosion are significant and increasing problems in many parts of the world. They are typically caused by climatic change, rapidly increasing population, shortage of water and loss of agricultural land to development. This process often places unprecedented pressure for increased productivity from a diminishing and non-renewable land resource. This often leads to contamination of the soil with salts (from contaminated irrigation water and fertiliser use) which eventually makes it impossible to grow food or even cover crops. This in turn accelerates soil degradation and leads to desertification.
One of the few ways to reverse salination is to irrigate contaminated soils with clean water to wash-out the saline contaminants. This is often not possible due to the lack of pure water. An alternative is to establish salt tolerant species (e.g. pistachio, barley and sugar beet), then to minimise water use, and subsequently to xe2x80x98soak-upxe2x80x99 salts in the harvested crops. This is a gradual process which will allow a wider range of less tolerant crops to be grown in the longer term.
Various proposals have been made for providing seed germination media which provide the seeds with water, nutrients and protection during the germination phase.
U.S. Pat. No. 5,189,833 discloses an arrangement in which lawn grass seeds are germinated in a thin layer of growing medium sprayed over a mat of non-woven polypropylene lying on top of an impermeable membrane. After a few days of germination, the mat carrying the seed-bearing medium can be lifted, rolled and then spread over an appropriately conditioned and prepared lawn bed. It will be appreciated that such an arrangement is neither intended nor suitable for growing crops in adverse environmental conditions.
Australian Patent Application AU-A-81394/75 discloses a seed bearing mat comprising upper and lower layers bonded together with a latex adhesive, seeds being bonded between the layers. The lower layer is a water permeable material such as straw, coconut fibres, peat moss or wood shavings whilst the upper or covering layer is formed from material of a finer texture than the lower layer such as coconut fibre dust or sawdust bonded together by latex. The seed bearing mat of AU-A-81394/75 is described as being particularly useful in preparing lawns.
French Patent Application FR-A-2505607 discloses a seed germination medium comprising a folded layer of a transparent plastics material such as polyethylene having bonded to the underside thereof bands of a water-soluble or degradable seed-bearing medium such as paper. In use, the seeds germinate beneath the transparent plastics layer and, as the seedlings grow, they lift the transparent layer away from the water-soluble/degradable medium. Thus the transparent layer is gradually unfolded and carried upwards by the growing seedlings and therefore remains in place over the top of the plants to maintain a greenhouse effect.
French Patent Application FR-A-2440438 discloses a peat-based seed bearing medium comprising a lower layer formed of a water-permeable fibrous material such as cellulose fibres or muslin cloth, an intermediate layer of peat comprising seeds and any additives; and optionally an upper layer which is also water-permeable and can be formed from a material such as muslin. Although FR-A-2440438 discloses that the media are envisaged as being economical for large scale use such as plantations in arid regions e.g. deserts, it is also emphasised that an advantage of the peaty medium, compared with polyethylene sheets, is that it allows the penetration of rain water.
International Patent Application WO-A-96/28010 discloses a seed germination medium in sheet form having upper and lower layers and seeds disposed therebetween. The upper and lower layers are preferably formed from a biodegradable paper material. In order to assist anchoring of the medium in the underlying soil or, in the case of desert areas, sand, the medium is slit longitudinally to enable it to be stretched laterally to form an open lattice. However, it has been found that a problem with the lattice arrangement disclosed in WO-A-96/28010 is that it has a tendency to dry out too quickly. In particular, when stretched to open out the lattice, the edges of the lattice openings lift exposing the lower layer of the medium and increasing water loss. Also, the lifting of the edges of the lattice results in the seeds being lifted away from the soil which acts to inhibit germination of the seedlings, possibly through build up of ethylene in the medium.
It is an object of the present invention to provide a seed germination medium which avoids the problems inherent in many known media and which enables seeds to be germinated effectively in a range of different types of environment, particularly arid and semi-arid areas and areas in which soil salination and desertification has taken hold.
Accordingly, in a first aspect, the invention provides a seed-germination medium comprising an upper layer formed from a biodegradable material which is permeable to gases but substantially impermeable to water in liquid form; a lower layer formed from a water-absorbent biodegradable material; seeds being disposed beneath the upper layer; and the upper layer having a plurality of perforations therein to enable seedlings germinating from the seeds to grow therethrough.
The lower layer is also preferably provided with a plurality of perforations to enable roots emerging from the seeds to grow therethrough.
The biodegradable material from which the upper layer is formed can be partially permeable to water vapour but should nevertheless provide some barrier properties with respect to water vapour. A major function of the upper layer is to minimise loss of water from the medium through evaporation, and to hold seeds in position when exposed to wind, rain or harsh irrigation.
The biodegradable material of the upper layer is preferably a biodegradable polymer. The polymer can be one which contains a biodegradable element and a non-biodegradable element. For example, the polymer can contain, as the non-biodegradable element, a polymer which, in its pure form is impermeable to water, for example polymers such as polyolefins, e.g. polyethylene and polypropylene; polyesters, polyamides, and chlorinated polymers such as polyvinylchloride (PVC). The upper layer can be made of a transparent polymeric material or it can be non-transparent.
The biodegradable element can function as a binder for the non-biodegradable element. Preferably the biodegradable polymer is one which is at least partially degraded by microbial means. For example, the biodegradable polymer can be a material such as a polysaccharide, e.g. starch, a phosphatide, or a glyceride, e.g. a mono-, di- or triglyceride or mixtures thereof such as a vegetable oil, one example of a vegetable oil being soya oil.
One example of a biodegradable material which can be used in the medium of the present invention is a composite material formed from PVC and soya bean oil sold by Linpac, France under the trade name xe2x80x9cDegradylxe2x80x9d. Another example of a suitable biodegradable polymer is a starch based polymer available from I.C.I. under the trade name xe2x80x9cBioplastxe2x80x9d.
In an alternative embodiment, the upper layer can be formed predominantly from a biodegradable water permeable material treated to render the upper surface thereof impermeable to liquid water, but partially permeable to water vapour, an example of such a material being a waxed paper.
The lower layer is an absorbent layer which can be made from a wide range of bio-degradable materials including air-laid paper e.g. an air-laid latex bonded paper, for example a paper formed from fluff pulp and a latex binder; waste or recycled paper; or other fibre-based or waste products. The selection of a suitable absorbent material for the lower layer will be dependent on cost, availability of raw materials and water for irrigation; the soil type, irrigation method, degree of capillarity required and the amount of water which must be retained in the medium to facilitate establishment of the seedling. In one preferred embodiment, 38-150 gm/m2 air-laid paper is used to form the lower layer, one such form of materials being available from Walkisoft of Steinfurt, Germany. Such air-laid papers typically contain approximately 85% fluff pulp and 15% latex binder, although greater or lesser amounts of binder can be used as desired.
Where availability of water is not a limiting factor, the lower layer may be relatively non-absorbent, e.g. may be formed from newsprint or other recycled material.
The lower layer can be a single layer or it can comprise a plurality, e.g. two, three or four, of layers. As with the upper layer, the lower layer can be performed to assist the penetration of roots emerging from the seeds, although with plants exhibiting strong root growth, this may be unnecessary. The lower layer can advantageously be coloured or treated to manipulate climatic conditions (e.g. to absorb or reflect heat) and to suppress weed growth below the medium. For example, the medium, or at least the surfaces thereof, can be provided in a variety of colours to assist soil warming/cooling or to exclude light so as to suppress weed growth and aid plant establishment. The medium may have different colours on its upper and lower surfaces to enhance or reduce the absorption of radiation on one surface and produce the opposite effect on its other surface.
The perforations in the upper and lower layers are preferably not in register, thereby ensuring that the medium cannot be expanded to form a lattice in the manner disclosed in WO-A-96/28010. The perforations can be slits or holes of any shape but, in the upper layer, preferably they are in the form of slits. The upper and lower layers can have different numbers of perforations, and the perforations in the respective layers can be of the same general shape or a different shape.
Where the perforations on the upper layer are in the form of slits, they can be for example from about 1 mm to about 5 mm long. The density of the perforations can be, for example, up to about 50,000 per square meter, typically less than 5,000 and greater than 100, for example between 500 and 1,000 per square meter. Where the perforations are not in the shape of slits but are, for example, in the form of circular or ovoidal holes (e.g. needle holes of up to 1 mm diameter) or small rectangular holes (e.g. up to 1 mm wide), the density of perforations preferably is in the range from 500 to 50,000 holes per square meter, typically 1,000 to 10,000.
In one embodiment, the upper layer can be provided with longitudinal slits and the lower layer can be provided with circular or ovoidal slits, for example needle holes, or no perforations at all. The perforation density in the lower layer can advantageously be greater than the density in the upper layer.
It is particularly preferred that the upper layer is provided with slits such as longitudinal slits since it has been found that this assists degradation of the upper layer, the upper layer material tearing along the lines of slits.
The upper and lower layers typically are laminated or bonded together, the strength of the bond between the layers being such as to resist separation by forces exerted by the growing seedling. In this respect, the medium of the present invention is further distinguished from the arrangements disclosed in FR-A-2505607.
The upper and lower layers typically can be bonded together by means of an adhesive or by mechanical means. Bonding the upper and lower layers together ensures good contact and trans-laminar movement of water in the medium. The upper and lower layers should remain closely bonded during laying and the early stages of establishment until the roots of the seedlings have penetrated the lower layer.
Where the upper and lower layers are bonded by means of an adhesive, the adhesive preferably is one which is biodegradable. Preferred adhesives are those which do not significantly affect the absorbency of the lower layer or the semi-permeability of the upper layer. Bonding of the upper and lower layers creates a trans-laminar effect which greatly enhances the movement of water across the medium from an irrigation source. The use of a semi-permeable upper layer reduces water loss from the absorbent layer reducing water demand and thereby assist in arresting salination.
The adhesive is typically one which is non-phytotoxic, and most preferably is water-based. Examples of such adhesives are starch, starch derivatives, polyvinyl alcohol (PVA) and ethylene vinyl acetate (EVA), optionally in combination with other adhesives.
The thickness of the adhesive layer is such that is does not soak the lower layer thereby affecting its absorption capability, its shelf life and the ability of the medium to be rolled and unrolled.
In order to minimise interference between the adhesive and any other components beneath the upper layer, the adhesive may be arranged in a defined pattern, for example a series of discrete regions such as rows, other components as described below being disposed between the discrete regions of adhesive.
Although adhesive bonding between the layers is currently preferred, the upper and lower layers can be bonded together by mechanical means such as by stitching, or stapling, or by piercing one layer through the other. Heat bonding can also be used to bond the upper and lower layers together. In order to achieve heat bonding, the lower layer typically would need to be coated with a heat fusible plastics material in the manner typically used for example with tea bag tissue, a welding tool being used to compress together the areas of the upper and lower layers to be fused together.
In addition to the seeds, a range of optional material can be disposed beneath the upper layer.
For example, fertilizers, micro-nutrients (such as zinc, copper, boron, and seaweed extracts), plant growth promoters and hormones, pH-regulators such as lime and sulphur, salt binding agents such as gypsum (calcium sulphate) and adsorbents such as activated carbon can be incorporated into the medium either by formulating with the adhesive or by application directly to one or other of the internal surfaces as a spray, granule or dust. The pH-controlling agents can be used to control the acidity of the immediate environment, and agents such as gypsum and activated charcoal can minimise the impact of adverse chemical contaminants and salt in the soil or medium, as well as to improve germination, and/or to aid and accelerate plant establishment.
Water retaining substances and wetting agents, which can be synthetic or natural material (such as clay minerals, e.g. bentonite and zeolite clays, or gelatine products, or surfactants such as non-ionic, anionic, cationic and amphoteric surfactants or other wetting adjuvants), can be included to increase the water absorbency of the medium. Examples of such water-retaining substances include silica gels and so-called xe2x80x9csuper absorbentsxe2x80x9d such as super absorbent acrylic polymers. In the case of wetting agents, these assist in dispersing the water throughout the medium, and allow less absorbent forms of paper or other substrate to be used.
Pesticides, (e.g. herbicides, fungicides, insecticides and nematicides etc.) can be incorporated beneath the upper layer and preferably between the layers. Although pesticide/micro-nutrient treated seed can be used, the pesticides can alternatively or additionally be incorporated into, or adsorbed or absorbed onto, the medium. This may reduce the concentration of pesticide (and fertilizer) in direct contact with the seed allowing a broader range of products to be used at higher rates without causing phytotoxicity, reducing the requirement for field applications and dose of active ingredient.
The seeds and optionally seeding agents such as propagation agents of plant, animal and fungal origin can be bonded or held by physical pressure at a pre-determined density between the layers of the medium. The density of seeding will typically depend upon the required plant population and environmental or field factors, for example. The seeds can advantageously be treated with pesticides of the type referred to hereinabove.
Where the lower layer is formed from a plurality of sheets, each separate layer can be impregnated with or carry a different additive. Thus, for example, an upper sheet can carry the seeds whilst plant nutrients can be carried by an underlying sheet.
The medium of the invention can be provided with reinforcing means for increasing its physical strength. The reinforcing means can be made sufficiently robust to enable the use of the medium as a ground anchoring medium in, for example, civil engineering applications. In one embodiment, the reinforcing means can take the form of a mesh made from a metal or plastics material, or can take the from of a fibrous reinforcement, such as a fibrous mat.
Where reinforcing means are present, they are preferably secured to the upper surface of the medium, for example by means of adhesive bonding. By securing the reinforcing means to the upper surface, the medium is held firmly in place. Moreover, irrigation tubes can be placed between the reinforcing means and the medium, the reinforcing means holding the irrigation tubes in place for as long as is required, for example to enable long term maintenance. A particular application of such an arrangement is in the stabilization and maintenance of steep or otherwise unstable embankments such as road and rail embankments, or mining spoil or as a covering on waste disposal landfill sites.
In another aspect, the invention provides a process for stabilising an area of ground (e.g. an embankment, such as a road or rail embankment, or mining spoilage or industrial or domestic waste dump, such as a landfill site) which comprises securing to the ground a seed germination medium as hereinbefore defined.
Either reinforced or non-reinforced medium can be used to stabilise an area of ground but, in cases such as embankments (e.g. roadside embankments) where the ground may be particularly unstable, the reinforced medium may be preferable.
In a further aspect, the invention provides a process for making the medium as hereinbefore defined, the process comprising the steps of:
(i) providing a first web formed from a material which will constitute the lower layer;
(ii) optionally forming a plurality of perforations in the first web;
(iii) depositing seeds onto the first web;
(iv) providing a second web formed from a material which will constitute the upper layer;
(v) forming a plurality of perforations in the second web, where such perforations are not already present;
(vi) optionally depositing adhesive on one or both of the first and second webs; and
(vii) bonding the first and second webs together.
In a still further aspect, the invention provides apparatus for manufacturing a medium as hereinbefore defined, the apparatus comprising first and second support means for holding respectively the first and second webs as hereinbefore defined; a bonding station for bonding the first and second webs together; means for advancing the first and second webs towards the laminating station; a seed dispenser upstream of the laminating station for depositing seeds onto the first web; optionally adhesive depositing means upstream of the bonding station for applying adhesive to one or both of the webs (preferably the second web); and optionally means for perforating one or both of the first and second web prior to bonding to form the medium.
The bonding station can take the form of a pair of rollers, the first and second webs being conveyed through the nip between the rollers, for example after adhesive has been applied to one or both of the webs, the rollers exerting pressure on the webs to bring about bonding therebetween. The rollers preferably are relatively soft, or at least have a resilient surface, so that the seeds are not damaged as the webs pass between the rollers. Alternatively, bonding can be achieved by applying tension to the finished roll of medium. The adhesive can be deposited on the web(s) in the form of a spray (which can be for example an electrostatic spray), or by means of a roller or brushes. Preferably adhesive is deposited on the second web, and more preferably no adhesive is deposited on the first web. When bonding is to be carried out by mechanical means rather than by adhesive, such mechanical means can be provided at the bonding station.
The formation of the perforations in each web can be effected by passing the web over or through a cutter. The cutter can take the form of a pair of rollers, one having a plurality of cutting elements and the other having a plurality of complimentary recesses for receiving the cutting elements, the web being conveyed through the nip between the rollers.
In a still further aspect, the invention provides a cutter roller for use in the apparatus of the invention, the cutter roller having a plurality of axially spaced cutting elements (such as a cutter wheel), each cutting element having a plurality of cutting edges disposed around the circumference thereof, the cutting edges of the cutter roller being configured such that in use on a substrate they cut a line of spaced apart perforations, preferably elongate slits, into the substrate.
In one embodiment, the cutter roller comprises a drive shaft having mounted thereon a plurality of cutter wheels and a plurality of spacer elements, the spacer elements being interposed between adjacent cutter wheels so as to space the cutter wheels apart. The drive shaft can have one or more slots or protrusions or other keying means which cooperate with complimentary formations on the cutter wheels and optionally the spacers so as to hold at least the cutter wheels against relative rotation with respect to the drive shaft.
The cutter wheels have a plurality of cutting edges spaced (preferably regularly) around their circumference. The cutting edges are typically arcuate in form and can be arranged in either a continuous or discontinuous array. For example, in a discontinuous array, the cutter wheel can have a plurality of cutting edges separated by non-cutting edges of a smaller radius than the cutting edges, the cutting and non-cutting edges having substantially concentric radii. In a continuous array, the cutting edges can have, for example, a substantially sinusoidal form.
In another aspect, the invention provides an adhesive composition suitable for use in the matrices as hereinbefore defined, the adhesive comprising a water soluble or water dispersible adhesive polymer such as PVA and one or more (preferably two or more) agents selected from pesticides (for example herbicides, fungicides, insecticides, nematicides), plant micronutrients (such as zinc, copper, boron), organic and inorganic fertilisers, plant growth regulators (e.g. seaweed extract), plant growth promoters and hormones, buffering agents and pH regulators (e.g. lime and sulphur), and salt binding agents such as gypsum (calcium sulphate).